MEMS Microphone Accelerometer Wafer Integration
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Solution Overview
Problem
Capacitive microphones in mobile devices are sensitive to mechanical vibrations, leading to body noise interference, which cannot be effectively compensated by signal processing, and users face inconvenience in silencing phones quickly in undesirable situations.
Innovation Solution
A method for manufacturing a micromachined microphone and accelerometer from a wafer, where a one-dimensional accelerometer is integrated close to the microphone, sharing the same process flow and physical size, with optimized mass compliance product to suppress mechanical vibrations, allowing for body noise cancellation and enabling features like silent mode activation through phone movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a capacitive microphone is made with a membrane and back plate structure, then the microphone can detect sound pressure waves, but the microphone becomes sensitive to mechanical vibrations causing body noise
Solution Approach 1:
The wafer is divided into separate microphone layer and accelerometer layer, allowing independent optimization of each function. The microphone structure is segmented from the substrate to reduce vibration coupling, while the accelerometer is placed in a separate layer to detect and compensate for vibrations independently.
Solution Approach 2:
An accelerometer is introduced as an intermediary device to detect mechanical vibrations and provide compensation signals. The accelerometer acts as a mediator between the vibration source and the microphone, enabling active noise cancellation through signal processing.
2Measurement precision
If an accelerometer is added to cancel body noise, then the signal-to-noise ratio improves, but the device complexity increases
Solution Approach 1:
The accelerometer is merged with the microphone in a unified MEMS structure fabricated from the same wafer. Both devices share common fabrication processes, substrates, and packaging, reducing overall device complexity despite the added functionality.
Solution Approach 2:
The wafer fabrication process is designed to produce both microphone and accelerometer structures simultaneously, making the manufacturing process universal for both device types. This multi-functional approach eliminates the need for separate fabrication lines and reduces overall system complexity.
3Manufacturing precision
If the microphone and accelerometer are integrated from the same wafer, then manufacturing precision is improved, but the manufacturing process becomes more complex
Solution Approach 1:
Both microphone and accelerometer structures are prepared in advance during wafer fabrication before final assembly. The wafer is pre-patterned with multiple functional layers that will become both microphone and accelerometer components, ensuring precise alignment and reducing post-fabrication complexity.
Solution Approach 2:
The fabrication process uses parameter changes in the wafer structure (such as layer thickness, material composition, and pattern geometry) to differentiate between microphone and accelerometer regions. By controlling fabrication parameters spatially across the wafer, both devices are created with high precision using a unified process.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution improves the signal-to-noise ratio by reducing mechanical vibration sensitivity, enabling effective body noise cancellation and allowing features like automatic silencing or answering calls through phone movement without increasing the microphone's physical size or requiring additional masks.
Implementation Method 1
an important performance parameter of such a microphone is the sensitivity to structural born sound, which is governed by undesired relative movement between the membrane and the back plate due to mechanical vibrations acting on the microphone as a whole
Implementation Method 2
A modulation of the air gap between the membrane and the back plate due to sound pressure waves applied on the membrane result in an electrically detectable signal when using conductive materials for the membrane and the back plate. In this way, the membrane and the back plate, both provided with conductive surfaces, form a capacitor which capacity changes in relation to sound pressure waves applied to the membrane.
Data Source
AI summary
The invention relates to a method for manufacturing a micromachined microphone and an accelerometer from a wafer 1 having a first layer 2, the method comprising the steps of dividing the first layer 2 into a microphone layer 5 and into an accelerometer layer 6, covering a front side of the microphone layer 5 and a front side of the accelerometer layer 6 with a continuous second layer 7, covering the second layer 7 with a third layer 8, forming a plurality of trenches 9 in the third layer 8, removing a part 10 of the wafer 1 below a back side of the microphone layer 5, forming at least two wafer trenches 11 in the wafer 1 below a back side of the accelerometer layer 6, and removing a part 12, 13 of the second layer 7 through the plurality of trenches 9 formed in the third layer 8. The micromachined microphone and the accelerometer according to the invention is advantageous over prior art as it allows for body noise cancellation in order to minimize structure borne sound.